Add solution notes scaffold and sub-heading format

- roadmap.org: problems now have *** Python and *** C++ sub-headings,
  plus Notes: links to per-problem org files
- scaffold-notes.mjs: creates 199 note files in org/cpp/dsa/<topic>/
  with backlinks to roadmap.org
- 18 topic folders under org/cpp/dsa/ for NeetCode 150 problems
- Updated AGENTS.md with new conventions and workflow

AGENTS.md

@@ -34,6 +34,13 @@ Periodically review this file and suggest improvements to the user if you notice
 
 ## Subdirectories
 - `leetcode/` — NeetCode roadmap extractor (dependency graph + problem list). See `leetcode/AGENTS.md`.
+- `org/cpp/dsa/` — LeetCode solution notes, one file per problem, organized by topic (18 folders)
+
+## LeetCode Workflow
+- `leetcode/out/roadmap.org` — tracker only (`**` headings, `g c c` to toggle DONE)
+- `org/cpp/dsa/<topic>/<problem>.org` — your notes, solutions, flashcards
+- Each links to the other via org file links
+- Problem tags (`:easy:`, `:medium:`, `:hard:`) enable filtering with `/ t`
 
 ## Active Context
 <!-- AI assistant maintains this section. Keep under 20 lines. -->